Gas burners

ABSTRACT

A gas burner including an air distributor and gas injection means arranged so that gas passes across and mixes with air which has passed through orifices in the distributor thereby forming an inflammable mixture which is burnt close to the downstream surface of the distributor.

United States Patent 1 Cafferty et al.

GAS BURNERS Inventors: Michael .Cafferty, Leeds; Cecil William Jewitt, Otley, both of England Assignee:

Leeds, England Filed: May 1, 1972 Appl. No.: 249,276

Foreign Application Priority Data May 6, 1971 Great Britain 13478/71 US. Cl. 239/4255 Int. Cl B051) 7/06 Field of seal'chu George Bray & Company Limited,

[ Apr. 30, 1974 [56] References Cited UNITED STATES PATENTS 1,721,381 7/1929 Ellis 239/425 3,093,314 6/1963 Meyer.. 239/425 3,632,287 1/1972 Reed 239/4245 X Primary ExaminerRichard A. Schacher Attorney, Agent, or FirmBrisebois & Kruger [57] ABSTRACT I A gas burner including an air distributor and gas injection means arranged so that gas passes across and mixes with air which has passed through orifices in the distributor thereby forming an inflammable mixture which is burnt close to the downstream surface of the distributor.

15 Claims ll Drawing'Figures 1 GAS BURNERS This invention relates to gas burners and more particularly to a burner producing a high intensity flame.

All forms of gas burner require that a certain minimum amount of air be mixed with the gas so that the latter may be fully combusted. Known forms of burner have provision for all or part of this air to be mixed with the gas prior to the point of combustion. In cases where a slack or low intensity flame may be used, that is where the flame volume is large relative to the heat output, it is usual to have only a part of the air required mixed with the gas prior to combustion, with the remainder of the air being entrained by the flame. Such burners employ a gas injector through which gas flows into a mixing tube, the momentum of the gas flow entraining air into the tube. In those cases where a tight or high intensity flame is required, that is, where the flame volume is small relative to the heat output, it is usual for all of the air required to be pre-mixed with the gas and for this purpose relatively expensive air and gas metering and mixing systems are needed.

A major problem with burners where all or part of the air is mixed with the gas prior to combustion, is that an inflammable gas mixture exists upstream of the part of the burner on which the flame burns, namely the flameport. Consequently, precautions have to be taken in designing the latter to ensure that the flame does not light back, that is when the flame front penetrates the 'flameport and the gas/air mixture burns inside the burner. This circumstance leads to overheating, ultimate destruction of the burner and to fire risk.

A newgeneration of domestic appliances is currently emerging, primarily for central heating purposes, with emphasis on compactness. A fan has been incorporated in the appliance for the purpose of speeding up the discharge of combustion products, thus allowing the miniaturisation of flue gas terminals. Since the fan also has the capability of blowing or sucking air through the appliance, it has been proposed to use it to overcome the resistance inherent in compact heat exchanger design, and to produce a pre-mixed' gas/air supply to the burner flameport, thus giving a high intensity flame which together allow for optimum miniaturisation of the appliance.

According to the present invention a gas burner includes an air distributor formed with a plurality of orifices adapted to haveair forced therethrough and gas injection means arranged relative to the distributor so that, in use, gas passes across, and mixes with air which has passed through, the orifices, thereby producing an inflammable mixture adapted to be burnt immediately downstream of the orifices.

The distributor may be in the form of a plate which may be flat or formed into conical, cylindrical or other shape to suit the application.

Conveniently, the burner may incorporate a fan for blowing or sucking combustion air through the orifices.

The gas injection means may be in the form of a gas header or headers containing a number of gas outlet openings through which gas issues to spread uniformly over the downstream surface of the distributor.

Air flowing through the orifices mixes with gas flowing across the downstream surface of the distributor producing an inflammable mixture at the orifice tion and all commonly used fuel gases can be burned in this manner.

The orifices may be in the form of holes or slots and the pattern may be varied according to the shape of the burner and the distribution of flame or heat release required. In order to obtain optimum mixing of fuel and air, each segment or section of the pattern must have its own individual gas injector orifice. Heat releases of up to 2,000 BTUs/ins. of burner surface area can be achieved at noise levels acceptable by domestic appliance standards. This coincides with air flow velocities of up to 1,000 ft./min. Flame turbulence and noise increases with increasing air velocity and if noise is not important considerably higher heat releases can be achieved.

Usual heat exchanger design considerations define total air flows of between percent and 200 percent of the stoichiometric requirement for the particular fuel gas used, with a preferred range of about percent to percent. With these values in mind and in order to produce the most compact flames, it is necessary to ensure that diffusion of gas into the air columns occurs at the earliest stage. With hole diameters and slot widths greater than 0.060 inch, diffusion is slow even at lower air velocities and the flames break open with resultant quenching and poor combustion.

Uniform spreading of the gas over the downstream surface of the distributor is achieved by employing a multiplicity of gas injector openings arranged to inject fuel gas into the low pressure regions on the distributor surface between successive orifice patterns and is a function of gas stream momentum or injector pressure and the entrainment effect of adjacent air columns. The degree of spread obtainable and the consequent maximum spacing between adjacent gas headers is governed by the maximum injector pressure that can be employed without starvation of the nearest orifices due to excessive gas stream velocity and the maximum entrainment effect produced by the higher air velocities. With reference to domestic appliance consideration, spreads of about 3 inches are possible from a single header. Successive headers may be employed and with contra or opposed gas flow may be spaced at upto 6 inches centres where injector pressures up to 5 inches w.g. are used.

For optimum performance the spatial arrangement of the orifices must be such that the gas stream, in the direction of injection, follows a low pressure path without interruption to the furthest orifice. Spread is encouraged if the air flow density increases with the distance from the injector. This may be achieved by having a slot or hole pattern converging away from the injector or in the case of parallel rows of slots or holes by altering the air velocity distribution accordingly.

Diffusion of gas perpendicular to the flow direction into the air columns becomes ineffective at distances greater than 0.3 inch. At distances much less than 0.05

' inch combustion becomes poor due to turbulence and flame quenching. Where long slots are used as orifices,

air flow characteristics may be modified by insertion of obstructions across the air stream on the upstream side of the orifices to modify the air velocity profile across the slots with resultant increase of flame stability when the burner is being used with low flame speed gases at the higher air velocities.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings of which:

FIG. 1 is a schematic outline of an appliance incorporating one form of burner showing the position of the latter relative to a fan and heat exchanger;

FIG. 2 is a cross-section of the gas header and air distributor plate for the burner of FIG. 1 showing the position of the gas outlet openings relative to the plate, together with possible dispositions of flame stabilisers;

FIG. 3 is a plan view of this form of burner showing the pattern of orifices in the plate and the distribution of gas outlet openings in the header;

FIGS. 4 and 5 show alternative forms of burner where the air distributor is in the form of a cylinder;

FIG. 6 illustrates a rectangular plan burner;

FIG. 7 is a section of the burner shown in FIG. 6;

FIG. 8 shows a part-sectional side elevation of a further form of burner;

FIG. 9 is a plan view of the burner shown in FIG. 8;

FIG. 10 is a part sectional side elevation of a multiburner incorporating a number of burners of the general type illustrated in FIGS. 8 and 9; and

FIG. 11 is a plan view of the multi-burner shown in FIG. 10. 7

Referring to FIG. 1, the burner generally comprises a gas supply pipe 1 which divides into two or more branches 2, each of which opens into an annular gas header 3. The header 3 is provided with a number of gas outlet openings 4 which extend inwardly thereof. Arranged below the plane containing the openings 4 is an air distributor in the form of a circular flat plate 5 provided with a number of slots 6 shown in FIG. 3. The plate and header are mounted below a heat exchanger 7 and above a fan unit 8, respectively. In operation air is forced through the slots 6 by the fan unit 8 which, in-

- cidentally, may be arranged above the slots to suck air therethrough and mixes with gas flowing across the downstream face of the plate 5 producing an inflammable mixture at that face. When ignited, this mixture burns close to the surface with each slot forming a flameport. To increase flame stability, annular stabilising baffles 9 (see in particular FIG; 2) are arranged on the upstream side of the slots 6. The direction of flow of the air and combustion products is indicated by arrows A and C, respectively.

In the example illustrated in FIGS. 1 to 3, the gas outlet openings 4 are positioned between 0.020 inch and 0.20 inch above the surface of the plate 5 and are directed to flow across the plate at an angle of between t5 to the surface. The diameters of the gas outlet openings cannot be specified precisely because they are dependent upon the overall heat release required, the calorific value of the fuel gas and the gas pressure. In the particular example shown, they are 0.040 inch in diameter, but could vary between 0.010 inch and 0.10 inch diameter.

As shown in FIG. 3, the air distributor is in the form of a circular disc which is 8 inches in diameter with radially extending slots 6 in the plate at 5 intervals. The

gas header 3 is circumferentially disposed around the disc its gas outlet openings 4 being directed radially inwards at intervals of 5, each opening being centrally situated between two radially converging slots 0.04 inch wide. This arrangement allows the distribution of air flowing through the plate to conform to the distribution of gas across the plate in accordance with the principles discussed earlier.

The air distributor described above takes the form of a flat disc, but dependent on the shape of the heat exchanger and the distribution of heat release required other forms may be utilised. Thus, the distributor may have the form of a cone of variable angle and designs involving surfaces curved in two planes, for example, hemispherical in shape, may be used.

In the arrangement shown in FIG. 4, for example, the air distributor is in the form-of a cylinder 10. Here, the forced air flow is caused to move upwardly into the cylinder and then outwardly through slots 1 l, as shown by arrows A, by deflection baffle plates 12. The air emerging from the slots 1] mixes with gas fired upwardly along the outer circumference of the cylinder by a gas header 13 having gas openings 14. As shown, each of the latter directs a stream of gas along and between a corresponding pair of adjacent slots 11. Ignition of this inflammable mixture produces a cylindrical flame formation close and on the outer surface of the cylinder, combustionproducts escaping in the direction of arrows C. Annular stabilizing baffles 12a are arranged across the upstream side of the cylinder to promote flame stability.

FIG. 5 shows a modification of the cylindrical air distributor arrangement illustrated in FIG. 4. Here, the forced air flow is caused to move vertically upwards along the outer walls of the cylinder 10, and then inwardly into the cylinder through slots 11, as shown by arrows A, by deflection baffle plates 15. In this case air emerging from the slots 11 mixes with gas fired upwardly along the inner circumference of the cylinder by a gas header 16 having openings 17. As shown, each of the latter directs a stream of gas along and between a corresponding pair of adjacent slots 11. Ignition of this inflammable mixture produces a cylindrical flame formation within and close to the inner surface of the cylinder, combustion products escaping in the direction of arrows C. Annual stabilizing baffles 12b are arranged across the upstream side of the cylinder to promote flame stability.

FIGS. 6 and 7 show another variation in which the air distributor is in the form of a flat rectangular plate 18.

Here, air is forced through slots 19 in the plate where it mixes with gas fired across the downstream face by a gas header 20 having gas openings 21. It will be seen that each pair of adjacent slots converges away from a corresponding one of the openings 21. Ignition of the inflammable mixture produces a rectangular plane flame configuration close to the downstream face of the plate 18. Stabilizing baffles 22 are arranged across the upstream side of the plate to promote flame stability. Extended flat versions are also possible providing the arrangement of orifices and gas headers is in accordance with the previously discussed principles.

In the arrangement illustrated in FIGS. 8 and 9, the distributor 23 is again in the form of a cylinder. Here, the distributor is enclosed by a surrounding shroud 24 which is shaped so that air passing through the inlet 25 is directed through the longitudinal slots 26 where it mixes with gas injected into the cylinder by a gas header 27. The latter is provided with an inlet 28 and a number of outlet openings 29 each of which is disposed between a corresponding pair of adjacent slots 26. The forced air flow is indicated by the arrows A whilst the combustion products escape in the direction of arrows C.

FIGS. and 11 illustrate a multi-burner incorporating a number of burners of the general type shown in FIGS. 8 and 9. The individual burners 30 are grouped together in ring formation (see FIG. 11) and are supplied by respective gas headers 31 having outlets 32; the headers being supplied by a common manifold 33 having an inlet 34. Air is supplied to the distributors through a surrounding casing 35 having an inlet 36. Instead of forming each shroud individually as shown in FIGS. 8 and 9, it will be seen from FIGS. 10 and l 1 that all the shrouds 37 are formed in a single blank of material 38.

The disposition of all the distributors is variable. They may fire vertically upwards, downwards, in a horizontal direction or at any angle in between.

In the cited examples, the air orifices are co-planar with the gas diffusion flames. In some instances, however, particularly where the highest orifice densities are employed, it may be advantageous to have the plane of air orifices somewhat higher than the gas flow planes as by this means the minimum distance between air columns, for which gas distribution is interrupted, can be reduced.

In all the foregoing examples the pattern of air orifrees, the gas outlet configuration, the gas pressure and the total free area presented to the air flow are chosen to promote uniform and intimate mixing of the gas and air in order to ensure complete combustion and to provide ports on which mutually stabilizing flames can be formed.

The parameters discussed define burners for use in forced air systems having perforated surfaces of varying shape with open areas of between 10% and 35% of the total surface, consisting of co-planar or raised hole and/or slot patterns, individual holes and/or slots having diameters and/or widths of between 0.015 inch and 0.060 inch, with or without stabilizing baffles, together with single or multiple gas headers suitably disposed on the downstream surface providing a multiplicity of gas orifices of diameters between 0.01 inch and 0.1 inch firing in preferred directions across the surface from a position 0.020 inch to 0.20 inch above that surface and within an angle of :5 to the surface and providing overall gas orifice densities greater than one per square inch of total surface.

It will be understood from the examples described above that the heat input and the intensity of the flame can be varied to suit the particular application and all commonly used fuel gases can be utilised. Furthermore, because mixing of the gas and air takes place at the point of combustion, that is downstream of the flameport, the possibility of light back is eliminated.

We claim:

1. A gas burner comprising an air distributor formed with a plurality of slots, means for forcing air through the slots and gas injection means arranged between each pair of adjacent slotsfor injecting gas in a direction across the downstream side of the distributor and between, and longitudinally of the slots so that the gas diffuses into the air which passes through the slots and produces an inflammable mixture for burning immediately downstream of the slots.

2. A gas burner as claimed in claim 1 in which the gas injection means is in the form of at least one gas header containing a plurality of gas outlet openings through which gas issues to spread uniformly over the downstream side of the distributor.

3. A gas burner as claimed in claim 2 in which said slots are arranged in a predetermined pattern, each of said gas openings being arranged to direct gas across a given part of the pattern.

4. A gas burner as claimed in claim 1 in which the slots in each pair of adjacent slots converge towards each other in a direction away from their corresponding gas injection means.

5. A gas burner as claimed in claim 1 in which the distributor is in the formof a flat plate.

6. A gas burner as claimed in claim 5 in which the plate is rectangular.

7. A gas burner as claimed in claim 6 in which the slots extend transversely of the plate.

8. A gas burner as claimed in claim 5 in which the plate is circular.

9. A gas burner as claim in claim 8 in which the slots extend radially of the plate.

10. A gas burner as claim in claim 1 in which the distributor is in the form of a cylinder.

11. A gas burner as claimed in claim 10 in which the slots extend longitudinally of the cylinder.

12. A gas burner as claimed in claim 11 in which the cylinder is surrounded by a shroud, the side wall of which tapers towards one end of the cylinder so that air is directed through the cylinder from outside to inside.

the said burners are arranged in a circular array. 

1. A gas burner comprising an air distributor formed with a plurality of slots, means for forcing air through the slots and gas injection means arranged between each pair of adjacent slots for injecting gas in a direction across the downstream side of the distributor and between, and longitudinally of the slots so that the gas diffuses into the air which passes through the slots and produces an inflammable mixture for burning immediately downstream of the slots.
 2. A gas burner as claimed in claim 1 in which the gas injection means is in the form of at least one gas header containing a plurality of gas outlet openings through which gas issues to spread uniformly over the downstream side of the distributor.
 3. A gas burner as claimed in claim 2 in which said slots are arranged in a predetermined pattern, each of said gas openings being arranged to direct gas across a given part of the pattern.
 4. A gas burner as claimed in claim 1 in which the slots in each pair of adjacent slots converge towards each other in a direction away from their corresponding gas injection means.
 5. A gas burner as claimed in claim 1 in which the distributor is in the form of a flat plate.
 6. A gas burner as claimed in claim 5 in which the plate is rectangular.
 7. A gas burner as claimed in claim 6 in which the slots extend transversely of the plate.
 8. A gas burner as claimed in claim 5 in which the plate is circular.
 9. A gas burner as claim in claim 8 in which the slots extend radially of the plate.
 10. A gas burner as claim in claim 1 in which the distributor is in the form of a cylinder.
 11. A gas burner as claimed in claim 10 in which the slots extend longitudinally of the cylinder.
 12. A gas burner as claimed in claim 11 in which the cylinder is surrounded by a shroud, the side wall of which tapers towards one end of the cylinder so that air is directed through the cylinder from outside to inside.
 13. A gas burner as claimed in claim 1 in which obstructions are arranged on the upstream side of the slots.
 14. A multi-burner including a plurality of the burners as claimed in claim
 1. 15. A multi-burner as claimed in claim 14 in which the said burners are arranged in a circUlar array. 